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Chemical collection and stock control for UK schools, universities and hospitals

Copper(II) sulfate (CAS 7758-98-7): storage and disposal

Copper(II) sulfate is probably the most common coloured salt in school and college stores, held as blue pentahydrate crystals and as white anhydrous powder, and in pathology and histology labs as working solutions. It is classified as harmful if swallowed, irritating to skin and eyes, and very toxic to aquatic life with long lasting effects, which is why it needs the same specialist route as other hazardous salts.

CAS number
7758-98-7
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Harmful or irritant pictogramHarmful or irritant
  • Hazardous to the environment pictogramHazardous to the environment

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as general stock and apart from the items listed under "Do not store with".
  3. If you no longer need it, add it to your disposal list so it goes on the next collection.

Safe storage in a school or lab

Pentahydrate crystals in a big tub and a small jar of anhydrous powder often share one prep room shelf, and the two have to be told apart on the label. Keep both in a dry, labelled general store, dated on arrival and away from food grade supplies. Anhydrous powder takes water back, so its lid must be tight. Make-up solutions used in histology and pathology get their own labels. UN number 3288 applies. Do not store a jar near a sink because of the risk to aquatic life, and clear out old tubs of crystals left over from years of demonstrations.

How to tell it has deteriorated

Blue crystals that lose water turn to a white or pale powder at the surface, and the change is visible long before the jar is empty. A tub of pentahydrate left in a warm room often has a pale, dusty coating on the crystals. Anhydrous powder goes the other way: it starts white, and where damp reaches it the powder turns blue. Green crust on a metal cap or around the neck shows copper salts have crept out. Clumping, a faded label and an unknown date of receipt are the usual general faults, and any jar that has changed colour should be described as it is.

How it must be disposed of

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

Its very toxic effect on aquatic life drives the whole route. No copper sulfate, including a weak blue solution left over from a lesson, may go down a sink or drain, and it must not go to general waste or a skip either. It leaves by specialist collection as hazardous waste, with 16 05 06* the entry in a lab pack, 16 05 07* outside one and 18 01 06* for healthcare holders. List pentahydrate, anhydrous powder and each solution separately, with the strength of a solution if known, and note any jar that has changed colour.

Waste codes and transport details for Copper(II) sulfate
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Human healthcare setting18 01 06*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Common quantities we collect

Usually held as: anhydrous, pentahydrate, 0.5 M.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.

Where it is commonly held

Hazard statements

  • H302 Harmful if swallowed.
  • H315 Causes skin irritation.
  • H319 Causes serious eye irritation.
  • H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P270 Do not eat, drink or smoke when using this product.
  • P273 Avoid release to the environment.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • P332+P317 If skin irritation occurs: Get medical help.
  • P337+P317 If eye irritation persists: Get medical help.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.
  • P391 Collect spillage.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

What do we do with weak copper sulfate solution left after a practical?

Keep it in a labelled container for collection. It is classified as very toxic to aquatic life with long lasting effects, and a dilute solution may be less hazardous than the crystals but must not go to drain.

Why has our blue copper sulfate gone white?

The pentahydrate loses its water of crystallisation in warm, dry conditions and turns to a white or pale powder. It is still copper sulfate. Keep the lid on, label the jar by its form and describe its condition.

Can anhydrous and pentahydrate be kept together?

They can share a shelf but not a jar. Label each by form and date. The anhydrous powder takes water back and turns blue, so its lid has to be tight.

Why does a histology lab need to treat solutions separately?

Working solutions are made at various strengths and may be less hazardous than the solid, but they are still collected as chemical waste. Label each with name, strength and date so it can be described accurately.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula CuO4S. EC number 231-847-6.

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